1. Field of the Invention
This invention relates to magnetic disk drives. More particularly, the present invention relates to disk drives and components thereof that include a novel flex-to-board connector that electrically connects the heads of a head stack assembly with connection pads on the drive's printed circuit board assembly.
2. Description of the Prior Art and Related Information
Magnetic disk drives, such as those used for mass storage in personal computer systems are well known. Generally, such disk drives include a head disk assembly (HDA) and a controller printed circuit board (PCBA). The HDA includes a cover, a base, one or more disks and a head stack assembly (HSA). The HSA rotatably positions a slider (head) having one or more read and write transducers over a disk. The HSA is controllably positioned by a servo system to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (HGA) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect between the slider (via the drive's preamp) and the PCBA with minimal constraint on movement. A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. The slider is said to be “flying” over the disk when in this state.
The HSA is internal to the HDA in a very clean environment. The PCBA, however, is outside the HDA—and outside the clean environment. One problem faced by hard disk drive designers is how best to electrically connect the HSA to the PCBA without compromising the clean environment of the HDA, and to do so in a reliable, readily manufacturable and inexpensive manner. The head stack in a disk drive rotates around a pivot axis, and a flat flexible cable is required to allow for the pivot motion while maintaining the electrical connection. This requirement places the major surfaces of the flat flexible cable in a vertical orientation.
FIGS. 1, 2 and 3 show various aspects of conventional head stack assemblies and flexible cable to board connectors. Considering now FIGS. 1–3 collectively, the actuator assembly portion of the HSA is shown at 120. The conventional actuator assembly 120 includes an actuator body 38 from which one or more actuator arms 44 are cantilevered. Cantilevered from the actuator body 38 in the opposite direction from the actuator arms 44 is a coil portion 40. Extending from the body portion 38 is a flex cable guide 162. The flex cable guide 162 guides a flat flexible cable 152 away from the actuator and toward a flex bracket 154 that is configured to fit within a cutout 156 within the base of the disk drive. The flat flexible cable 152 carries electrical signals from the slider (via the preamp 87) to the PCBA 14. Toward that end, conventional disk drives typically guide the flat flexible cable 152 into a flex bracket such as shown at 154 and bend the flat flexible cable 152 into a horizontal orientation around the flex bracket 154 and solder the trace pads of the flexible cable 152 to a connector 155 attached to the flex bracket 154. Indeed, whereas the flat flexible cable 152 leaves the flex cable guide 162 in a vertical orientation (i.e., oriented in the y direction shown in FIG. 2), the flat flexible cable is bent 90 degrees (as best shown in FIG. 3 that shows a simplified representation of the underside of the flex bracket 154 and that of the connector 155 and the manner in which the flat flexible cable 152 is bent) into a horizontal orientation (i.e., oriented in the x direction shown in FIG. 2). The flat flexible cable 152 is conventionally soldered to the connector 155. Conventionally, a gasket seal 160 is interposed between the flex bracket 154 and the base. Screws, shown at 158 in FIG. 2, are conventionally used to force the flex bracket 154 and gasket seal 160 against the base so that the contacts 157 of connector 155 make compression contacts directly with the appropriate circuit board pads of the PCBA 14.
Such conventional designs have a number of disadvantages. For example, as the flat flexible cable 152 (a polyimide film with embedded conductive traces) must be bent around the L-shaped flex bracket 154, the flexible cable 152 must be cut in a corresponding L-shape. This shape reduces the number of such flat flexible cables that may be cut from a given rectangular sheet of such polyimide material. Another disadvantage relates to the screws 158. The use of such fasteners entails the need to create screw tap holes in the base. Moreover, the act of driving the screws 158 generates particulates that may adversely affect the operation of the drive. Eliminating the screws 158 would eliminate the risk of generating such particulates, as well as reduce component costs of the drive. Eliminating the need for the gasket seal 160 would also similarly reduce component costs and thus reduce the overall cost of the drive. In conventional HSAs, the flat flexible cable 152 is attached to the actuator assembly 120 as well as soldered to the connector 155. In practical terms, this means that the actuator assembly 120 includes the attached flex cable 152 as well as the soldered-on connector 155. The actuator assembly must then be pivotally installed on a pivot-bearing cartridge 34 and the flex bracket 154 must be fitted within a hole in the base so that the contacts 157 of the connector 155 may make electrical contact with pads on the PCBA 14. This hole in the base creates a potential leak path that increases the possibility of particulate or other contamination within the clean environment of the HDA.
Clearly, there is a need to redesign the interface between the HSA and the PCBA. Such an interface should address the above-discussed disadvantages of the conventional connector assembly, should forego the use of screws for cleanliness and drive reliability, should allow for simple assembly in a high volume process, should use inexpensive components, should provide reliable electrical contacts at the required impedance and should allow the connector to be grounded to the base, among other desirable characteristics.